In Chemistry, pH is the measure of the ion concentration in a liquid. It is used as a measure of the acidity or basicity of the fluids and body tissues.

Question

It is a most important concept in medicine and other sciences. Pure water has a pH value of about 7. Any thing with a pH value of less than 7 is considered an acid and anything with pH more than 7 is considered a base. As you may have guessed, pH is a log function: pH=−logH^+

where H^+ is the hydrogen ion concentration.

Note: the two letters 'pH' together stand for one variable. The letter and symbol 'H^+' stands for a different variable.

(a) Rain water before the industrial revolution had a pH of 5. Acid rain, or rain in the United States, now has pH of about 4. Has the hydrogen concentration in rainwater increased or decreased since the industrial revolution and by how much?

Note that you need to determine H^+ when pH is 5 and you need to determine H^+ when pH is 4 and then subtract to determine the amount of increase or decrease.


(b) The "life range" of blood in a person must be between 7.1 and 7.7. That means people with blood outside this "life range" are dangerously ill. How much can hydrogen ions fluctuate so that a person's pH is in the "life range"?

Note: Again you need to determine the two amounts of H^+ and subtract them.

Answer 1

(a)

 

Before the industrial revolution:

 

[H₃O⁺] = 10^-pH = 10^-5

 

Now:

 

[H₃O⁺] = 10^-pH = 10^-4

 

10^-4 - 10^-5 = 9 x 10^-5 ⇒ increase

 

(b)

 

10^-7.1 ≅ 7.943 x 10^-8

10^-7.7 ≅ 1.995 x 10^-8

 

Life range:

 

1.995 x 10^-8 ≤ [H₃O⁺] ≤ 7.943 x 10^-8